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The Human Body
The Human Body
The Heart
The Heart
Chambers of the Heart:
The heart is a muscular organ about the size of a fist, located just behind and slightly left of the breastbone. The heart pumps blood through the network of arteries and veins called the cardiovascular system.
The heart has four chambers:
The right atrium receives blood from the veins and pumps it to the right ventricle.
The right ventricle receives blood from the right atrium and pumps it to the lungs, where it is loaded with oxygen.
The left atrium receives oxygenated blood from the lungs and pumps it to the left ventricle.
The left ventricle (the strongest chamber) pumps oxygen-rich blood to the rest of the body. The left ventricle’s vigorous contractions create our blood pressure.
The coronary arteries run along the surface of the heart and provide oxygen-rich blood to the heart muscle. A web of nerve tissue also runs through the heart, conducting the complex signals that govern contraction and relaxation. Surrounding the heart is a sac called the pericardium.
Left and right sides
The left and right sides of the heart work in unison. The atria and ventricles contract and relax in turn, producing a rhythmic heartbeat.
Right side
The right side of the heart receives deoxygenated blood and sends it to the lungs.
The right atrium receives deoxygenated blood from the body through veins called the superior and inferior vena cava. These are the largest veins in the body.
The right atrium contracts, and blood passes to the right ventricle.
Once the right ventricle is full, it contracts and pumps the blood to the lungs via the pulmonary artery. In the lungs, the blood picks up oxygen and offloads carbon dioxide.
Left side
The left side of the heart receives blood from the lungs and pumps it to the rest of the body.
Newly oxygenated blood returns to the left atrium via the pulmonary veins.
The left atrium contracts, pushing the blood into the left ventricle.
Once the left ventricle is full, it contracts and pushes the blood back out to the body via the aorta.
What are the four main functions of the heart?
The four main functions of the heart are:
Pumping oxygenated blood to the other body parts.
Pumping hormones and other vital substances to different parts of the body.
Receiving deoxygenated blood and carrying metabolic waste products from the body and pumping it to the lungs for oxygenation.
Maintaining blood pressure
The Circulatory System
The Circulatory System
What is blood?
Blood, by definition, is a fluid that moves through the vessels of a circulatory system. In humans, it includes plasma (the liquid portion), blood cells (which come in both red and white varieties), and cell fragments called platelets.
Plasma is the main component of blood and consists mostly of water, with proteins, ions, nutrients, and wastes mixed in.
Red blood cells are responsible for carrying oxygen and carbon dioxide.
Platelets are responsible for blood clotting.
White blood cells are part of the immune system and function in immune response.
Red blood cells
Red blood cells
Red blood cells, or erythrocytes, are specialized cells that circulate through the body and deliver oxygen to tissues. In humans, red blood cells are small and biconcave (thinnest in the center, just 7-8 μm in size) and do not contain mitochondria or a nucleus when mature. These characteristics allow red blood cells to effectively perform their task of oxygen transport.
Small size and biconcave shape increase the surface area-to-volume ratio, improving gas exchange, while lack of a nucleus makes additional space for hemoglobin, a key protein used in oxygen transport. Lack of mitochondria keeps red blood cells from using any of the oxygen they’re carrying, maximizing the amount delivered to tissues of the body.
Platelets and clotting
Platelets and clotting
Platelets, also called thrombocytes, are cell fragments involved in blood clotting. They are produced when large cells called megakaryocytes break into pieces, each one making 2000-3000 platelets as it comes apart. Platelets are roughly disc-shaped and small, about 2-4 μm in diameter.
White blood cells
White blood cells
White blood cells, also called leukocytes, are much less common than red blood cells and make up less than 1% of the cells in blood. Their role is also very different from that of red blood cells: they are primarily involved in immune responses, recognizing and neutralizing invaders such as bacteria and viruses. White blood cells are larger than red blood cells, and unlike red blood cells, they have a normal nucleus and mitochondria.
Arteries and Veins
Arteries and Veins
Arteries are blood vessels responsible for carrying oxygen-rich blood away from the heart to the body. Veins are blood vessels that carry blood low in oxygen from the body back to the heart for reoxygenation.
Arteries and veins are two of the body’s main type of blood vessels. These vessels are channels that distribute blood to the body. They’re part of two closed systems of tubes that begin and end at the heart. These systems of tubes are either:
Pulmonary. The pulmonary vessels are arteries that transport oxygen-poor blood from the heart’s right ventricle to the lungs. Pulmonary veins transport oxygen-rich blood back to the heart’s left atrium.
Systemic. The systemic vessels are arteries that carry oxygen-rich blood from the heart’s left ventricle to the tissues in all parts of the body. They then return oxygen-poor blood through the veins back to the heart’s right atrium.
The Circulatory System
The Circulatory System
The circulatory system is composed of the heart and blood vessels, including arteries, veins, and capillaries.
Our bodies actually have two circulatory systems: The pulmonary circulation is a short loop from the heart to the lungs and back again, and the systemic circulation (the system we usually think of as our circulatory system) sends blood from the heart to all the other parts of our bodies and back again.
The heart has four chambers that are enclosed by thick, muscular walls.
It lies between the lungs and just to the left of the middle of the chest cavity.
The bottom part of the heart is divided into two chambers called the right and left ventricles, which pump blood out of the heart. A wall called the septum divides the ventricles.
The upper part of the heart is made up of the other two chambers of the heart, the right and left atria. The right and left atria receive the blood entering the heart.
A wall called the septum divides the right and left atria, which are separated from the ventricles by the atrioventricular valves.
The tricuspid valve separates the right atrium from the right ventricle, and the mitral valve separates the left atrium and the left ventricle.
Arteries carry blood away from the heart. They are the thickest blood vessels, with muscular walls that contract to keep the blood moving away from the heart and through the body.
In the systemic circulation, oxygen-rich blood is pumped from the heart into the aorta. This huge artery curves up and back from the left ventricle, then heads down in front of the spinal column into the abdomen.
Two coronary arteries branch off at the beginning of the aorta and divide into a network of smaller arteries that provide oxygen and nourishment to the muscles of the heart.
Unlike the aorta, the body’s other main artery, the pulmonary artery, carries oxygen-poor blood. From the right ventricle, the pulmonary artery divides into right and left branches, on the way to the lungs where blood picks up oxygen.
The circulatory system carries oxygen, nutrients, and hormones to cells, and removes waste products, like carbon dioxide and urea.
When blood circulates in the body, it enters the heart through the right atrium, passes through to the right ventricle, and flows out through the pulmonary artery to the lungs, where it picks up oxygen and gets rid of carbon dioxide.
From the lungs, blood returns to the left atrium and then enters the left ventricle, where it is pumped to the body through the aorta.
The respiratory system
The respiratory system
Purpose of Gas Exchange
Purpose of Gas Exchange
Purpose of gas exchange: To transfer oxygen from the atmosphere to tissues of the body, and to move metabolically produced carbon dioxide from tissues of the body to the atmosphere body to the atmosphere.
Structures involved in Gas Exchange
Structures involved in Gas Exchange
Passage of air into the lungs
Passage of air into the lungs
Air enters the body and is warmed as it travels through the mouth and nose.
It then enters the trachea.
The trachea divides into two bronchi. One bronchus enters each lung.
Each bronchus branches out into smaller tubes called bronchioles. Air travels through these bronchioles.
At the end of the bronchioles, the air enters one of the many millions of alveoli where gaseous exchange takes place.
Parts of the Respiratory System
Parts of the Respiratory System
Your respiratory system includes your:
Nose and nasal cavity
Sinuses
Mouth
Throat (pharynx)
Voice box (larynx)
Windpipe (trachea)
Diaphragm
Lungs
Bronchial tubes/bronchi
Bronchioles
Air sacs (alveoli)
Capillaries
Mouth and nose: Openings that pull air from outside your body into your respiratory system.
Pharynx (throat): Tube that delivers air from your mouth and nose to the trachea (windpipe).
Trachea: Passage connecting your throat and lungs.
Bronchial tubes: Tubes at the bottom of your windpipe that connect into each lung.
Lungs: Two organs that remove oxygen from the air and pass it into your blood.
From your lungs, your bloodstream delivers oxygen to all your organs and other tissues.
Muscles and bones help move the air you inhale into and out of your lungs. Some of the bones and muscles in the respiratory system include your:
Diaphragm: Muscle that helps your lungs pull in air and push it out.
Ribs: Bones that surround and protect your lungs and heart.
Aerobic respiration needs oxygen, and it produces carbon dioxide as a waste product. The human respiratory system contains the organs that allow us to get the oxygen we need and to remove the waste carbon dioxide we do not need. It contains these parts:
two lungs
tubes leading from the mouth and nose to the lungs
various structures in the chest that allow air to move in and out of the lungs
Connecting the outside to the inside
Connecting the outside to the inside
Air passes from the mouth into the trachea, often called the windpipe. The trachea divides into two bronchi, with one bronchus for each lung.
Each bronchus divides further in the lungs into smaller tubes called bronchioles. At the end of each bronchiole, there is a group of tiny air sacs. These air sacs have bulges called alveoli to increase their surface area.
Breathing involves movements of the ribs, intercostal muscles and diaphragm to move air into and out of the lungs:
when we breathe in, we inhale
when we breathe out, we exhale
Structure of Lungs
Structure of Lungs
The lungs begin at the bottom of your trachea (windpipe). The trachea is a tube that carries the air in and out of your lungs. Each lung has a tube called a bronchus that connects to the trachea. The trachea and bronchi airways form an upside-down “Y” in your chest. This “Y” is often called the bronchial tree.
The bronchi branch off into smaller bronchi and even smaller tubes called bronchioles. Like the branches of a tree, these tiny tubes stretch out into every part of your lungs. Some of them are so tiny that they have the thickness of a hair. You have almost 30,000 bronchioles in each lung.
Each bronchiole tube ends with a cluster of small air sacs called alveoli (individually referred to as alveolus). They look like tiny grape bunches or very tiny balloons. There are about 600 million alveoli in your lungs. The small bubble shapes of the alveoli give your lungs a surprising amount of surface area — equivalent to the size of a tennis court. This means there’s plenty of room for vital oxygen to pass into your body.
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